The embodiments described herein generally relate to wireless communications on-board aircraft. More particularly, they relate to a method for controlling an on-board aircraft network cell to be used in an on-board aircraft wireless communication network, to such an on-board aircraft network cell to be used in an on-board aircraft wireless communication network, to an on-board aircraft wireless communication network comprising at least one such on-board aircraft network cell, and to an aircraft comprising such on-board aircraft wireless communication network.
Reliable radio access techniques for packet switching wireless communication networks are well specified in standards, such as IEEE (Institute of Electrical and Electronics Engineers) 802.15.4, WirelessHART (Wireless Highway Addressable Remote Transducer Protocol) protocol or ISA (International Society of Automation) 100.11a.
For instance, IEEE 802.15.4 relates to the physical layer and media access control for low-rate wireless personal area networks (LR-WPANs), or the WirelessHART protocol pertains to a time synchronized, self-organizing, and self-healing mesh architecture. The protocol may support operation in the 2.4 GHz Industrial, Scientific and Medical (ISM) band using e.g. IEEE 802.15.4 standard radios. Finally, ISA 100.11a pertains to Wireless Systems for Industrial Automation, in particular to Process Control and Related Applications.
However, none of the above-cited techniques considers redundancy in space, time and/or frequency, especially in order to increase the reliability of wireless communication networks on-board aircraft to meet airworthiness standards.
Accordingly, there is a need for a reliable and robust radio channel access technique on-board aircraft.
In a first embodiment, a method for controlling an on-board aircraft network cell is provided. The on-board aircraft network cell is configured to be used in an on-board aircraft wireless communication network. The on-board aircraft network cell comprises at least one Wireless Module (WM) unit and at least two Wireless Data Concentrator (WDC) units. The method comprises establishing at least two independent wireless links, each between the at least one WM unit and one of the at least two WDC units.
The at least two WDC units may be spatially separated. In this respect, the at least two WDC units may also be referred to as at least two spatially separated WDC units. The on-board aircraft wireless communication network may comprise two or more of such on-board aircraft network cells, e.g., a plurality of such on-board aircraft network cells. In accordance therewith, the method may equally be performed in an on-board aircraft network comprising at least one such on-board aircraft network cell.
The on-board aircraft network cell comprising at least two spatially separated WDC units, allows a WM unit inside such cell to communicate with the at least two WDC units (and thereby with an on-board server connected thereto) via two or more wireless links (also called communication links), one link for each WDC unit inside the cell. A WM/WDC may only use one of these wireless links at a time, e.g., for wireless transmission of a data packet from the WM to the WDC or vice versa. Alternatively, for multicast transmissions, a WM/WDC may use two or more of these wireless links at a time, as will be described in more detail below. Independent of the number of wireless links used, a wireless link may be associated with a WM unit, a WDC unit (space), a specific time slot (time), a radio channel (frequency) and a transmission direction as will be described in more detail below.
The method may comprise organizing channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links inside the on-board aircraft network cell or in each of two or more on-board aircraft network cells. An on-board aircraft network cell may contain multiple, e.g., hundreds, of WM units. The WM units and/or the WDC units may have specific communication demands. Further, an on-board server unit connected to the WDC units may have specific communication demands. By organising (or coordinating) the (radio) channel access of the at least one WM unit and the at least two WDC units inside a cell, collisions on the (radio) channel can be avoided, and/or communications reliability and robustness can be increased. The (radio) channel access may be organized in space, time and/or frequency (i.e., up to three dimensions).
The method may comprise scheduling channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links. Scheduling may be understood as the organisation of the channel access by assigning the available at least two wireless links to the available resources in time, frequency and/or space by means of one or more of the multiple access and diversity techniques described below. The above-mentioned organization of the (radio) channel in space, time and/or frequency may be used by scheduling the wireless links, which represent a (packet) transmission, by assigning the right attributes. In short, the organization of the (radio) channel in space, time and/or frequency may be understood as or may be performed (carried out) by scheduling transmissions on the wireless links. A schedule created by the scheduling may use a wireless link several times on different time slots to coordinate packet transmission between a WM unit and a WDC unit in order to fulfil specific communications demands.
The scheduling may comprise selectively using one or more of Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Space Division Multiple Access (SDMA) techniques for channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links. These techniques used to organize the access to the (radio) channel (or to schedule access to the channel) for a manifold of users are called multiple access techniques. TDMA may organize the (radio) channel of multiple users in time. For example, using TDMA, a first WM unit can be scheduled to transmit in a first time slot to a first WDC unit, a second WM unit can be scheduled to transmit in a second time slot to a second WDC unit, and the first WM unit can be scheduled to transmit in a third time slot to the first WDC unit. The scheduled transmissions in TDMA do not necessarily have to be on the same (radio) channel. FDMA may organize the (radio) channel access of multiple users in frequency. For example, a first WM unit may be scheduled to transmit on a first channel in a first time slot to a first WDC unit, and a second WM unit may be scheduled to transmit on a second channel in the first time slot to a second WDC unit. SDMA may organize the radio channel access in space. For example, a first WM unit may be scheduled to transmit on a first channel in a first time slot to a first WDC unit, and a second WM unit may be scheduled to transmit on the first channel in the first time slot to a second WDC unit on a different wireless link, if mutual interference between the transmissions is acceptable. Combination of two or more multiple access techniques is possible.
The method may comprise selectively using one or more of spatial diversity, frequency diversity and time diversity techniques for channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links.
As stated above, multiple access techniques may be used to organize the (radio) channel access of multiple users. Diversity techniques may be used to increase the communication robustness/reliability between a signaling WM unit and an on-board server unit being connected to the at least two WDC units. Diversity may be established by using multiple access techniques. By using spatial diversity, a first WM unit may be scheduled to transmit the same information to different WDC units (e.g., different spatial locations) at the same time via different communication links (this can be also referred to as Multicast) or at different times. In the latter case, a first WM unit may be scheduled to transmit a packet, via a wireless link, to a first WDC unit in a first time slot on a first channel, and then the first WM unit may transmit the same packet, via a different wireless link, to a second WDC unit in a second time slot on the first channel. Spatial diversity can be used to counteract the spatial blockage of the radio channel. By means of frequency diversity, a first WM unit may transmit the same information on different channels. This may happen at different times. For example, a first WM unit may be scheduled to transmit a packet, via a wireless link, to a first WDC unit in a first time slot on a first channel. Then, the first WM unit may transmit the same packet, via the same wireless link, to the first WDC unit in the second time slot on a second channel. Frequency diversity counteracts bad conditions on a single radio channel, e.g., on the first channel. By way of time diversity, a first WM unit may transmit the same information in different time slots. For example, a first WM unit may be scheduled to transmit a packet, via a wireless link, to a first WDC unit in a first time slot on a first channel. Then, the first WM unit may transmit the same packet, via the same wireless link, to the first WDC unit in a third time slot on the first channel. Time diversity counteracts the temporary blockage of e.g. a communication link. A combination of two or more diversity techniques is possible.
The method may comprise selectively combining two or more of TDMA, FDMA, SDMA, spatial diversity, frequency diversity and time diversity techniques for channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links. The specific network cell topology as mentioned above, i.e., multiple WDC units per WM unit, enables the combined usage of TDMA, FDMA, and SDMA to organize the (radio) channel access. Additionally or alternatively, due to the specific network cell topology as mentioned above, it is possible to combine spatial, frequency and time diversity techniques, for example by using a combination of TDMA, FDMA and SDMA techniques, to increase communication robustness/reliability. The combined usage of two or more multiple access and/or diversity techniques can be ensured by appropriate scheduling of the (radio) channel access as explained above.
The method may comprise developing a schedule for scheduling channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links based on requirements on data rate, delay time, quality of service (QoS), reliability and/or robustness demanded by on-board aircraft components operating the at least one WM unit. For example, the requirements on data rate, delay time, QoS, reliability and/or robustness demanded by the on-board aircraft components may be determined or acquired and the schedule may be determined in accordance therewith. The schedule may be considered to describe the channel access on the at least two wireless links by means of one or more of the above-mentioned multiple access and diversity techniques. The schedule may be derived by a self-organizing, distributed or centralized algorithm. The schedule may be dynamically changed.
According to a second embodiment, a computer program may be provided. The computer program may be stored on at least one of the at least one WM unit, the at least two WDC units and any other suitable device such as the on-board server unit. The computer program comprises program code portions for carrying out one or more of the aspects described herein, when the computer program is run or executed on a computing device such as a microprocessor, a microcontroller or a digital signal processor (DSP) or the like.
In a third embodiment, an on-board aircraft network cell is provided. The on-board aircraft network cell is configured to be used in an on-board aircraft wireless communication network. The on-board aircraft network cell comprises at least one Wireless Module (WM) unit, at least two Wireless Data Concentrator (WDC) units, and at least two independent wireless links. Each wireless link is established between the at least one WM unit and one of the at least two WDC units.
The on-board aircraft network cell may also be referred to as a network cell on-board an aircraft. Likewise, the on-board aircraft wireless communication network may also be referred to as a wireless communication network on-board an aircraft. In telecommunication, the term wireless data concentrator, or in short just concentrator, may be understood as a device that provides one or more WMs with access to a wired onboard-network.
The at least one WM unit may be, for example, any conceivable network element that can be arranged in or can be integrated into the on-board aircraft wireless communication network. The at least one WM unit may be configured to exchange information with other WM units of the on-board aircraft wireless communication network via one or more WDCs. For instance, in principle all sensors and/or actuators conventionally linked up by wire-bound communication can also be integrated in wireless manner into the on-board aircraft wireless communication network as WM units or can be linked up to the associated systems (such as WDC units). As examples of such WM units, temperature sensors, pressure sensors, proximity switches, speed sensors, airflow meters, position-measuring devices, indicating elements, electric motors, lamps and illumination systems may be mentioned.
The at least two WDC units may be in wireless communication with the at least one WM unit. For example, the at least two WDC units may be in wireless communication with two or more WM units. The at least two WDC units may be respectively configured in such a way that they are in communication with all WM units that are located in its coverage zone. This coverage zone may also be referred to as the on-board aircraft network cell mentioned above. The WDC units may be arranged at different places in the on-board aircraft wireless communication network.
By providing at least two WDC units in the on-board aircraft network cell for the at least one WM unit, thereby providing at least two independent wireless links for communication with an onboard-server such as an avionics server, wireless communication capacity, reliability and robustness of (organization of) radio channel access inside the on-board aircraft wireless communication network (wireless communication network on-board the aircraft) may be increased.
If, in the below, it is stated that the on-board aircraft network cell or, in short, the network cell, is configured to perform or carry out certain method steps or procedures, this may imply that at least one of the (i) at least one WM unit, (ii) the at least two WDC units, and (iii) one or more further units such as a server unit or other control unit may be configured to perform or carry out such method steps or procedures.
By providing at least two WDC units in the on-board aircraft network cell for the at least one WM unit, thereby providing at least two wireless links for communication with an onboard-server such das an avionics server, multiple access techniques may selectively be used alone or in combination for channel access of at least one of the at least one WM unit and the at least two WDC units to one or more of the at least two wireless links. Such multiple access techniques may comprise TDMA, FDMA and SDMA techniques.
As stated above, TDMA techniques may be used in the on-board aircraft network cell for scheduling transmissions via the at least two wireless links. In accordance therewith, time may be partitioned into time slots. Such time slots can be accessed for transmission. The network cell may further be configured to schedule one of the time slots per each wireless link (each wireless link of the at least two wireless links). The network cell may be configured to partition the time slots so as to each have the same time length or to have mutually different time lengths.
As stated above, FDMA techniques may be used in the on-board aircraft network cell for scheduling transmissions via the at least two wireless links. If FDMA techniques are used, the network cell may be configured to partition an available frequency range into a predetermined number of independent channels for transmission. The network cell may further be configured to tune the respective WDC unit and respective WM unit assigned to the wireless link to the same channel. The size of the channels may be fixed.
As stated above, SDMA techniques may be used in the on-board aircraft network cell for scheduling transmissions via the at least two wireless links. In that case, the network cell may be configured to simultaneously use the at least two wireless links for data transmission. For example, the at least one WM unit may be configured to simultaneously transmit data to the at least two WDC units via the at least two wireless links assigned to the at least one WM unit. Alternatively or additionally, the at least two WDC units may be configured to simultaneously transmit or to transmit data at different times to two or more WM units via the at least two wireless links assigned to the respective WM units.
One or more diversity techniques may be used in the on-board aircraft cell. As stated above, such diversity techniques may comprise time diversity, frequency diversity, and spatial diversity. Alternatively or additionally, frequency hopping techniques may be used, e.g., by (rapidly) switching a carrier among two or more, e.g., several, frequency channels. In the case that one or more diversity techniques are used, wireless communication capacity, reliability and robustness of (organization of) the radio channel access inside the on-board aircraft wireless communication network on-board the aircraft may be increased even further. If time diversity involves TDMA techniques, all advantages of time diversity may be exploited, such as little resource allocation due to time sharing. If frequency diversity involves at least one of FDMA and frequency hopping techniques, all advantages of frequency multiplexing can be exploited, such as simultaneous transmission in different bands (channels) or quick/flexible tunability between channels. If spatial diversity involves SDMA techniques, all advantages of true redundancy may be exploited, such as fail-safe redundancy due to the doubled WDC units, true simultaneous transmission, separation of uplink/downlink etc.
Each of the at least two wireless links may comprise a link number to uniquely identify the wireless link connection between one WM unit of the at least one WM unit and one WDC unit of the at least two WDC units. By assigning link numbers to the at least two wireless links, it is possible to schedule channel access in the on-board aircraft network cell described above by means of one or more of the above-mentioned multiple access and diversity techniques. Alternatively or additionally, each of the at least two wireless links may comprise a link direction. The link direction may be one of a downlink (DL) for transmission from one WDC unit of the at least one two WDC units to one WM unit of the at least one WM unit, and an uplink (UL) for transmission from one WM unit of the at least one WM unit to one WDC unit of the at least two WDC units. By assigning link directions to the at least two wireless links, it is possible to schedule channel access in the on-board aircraft network cell described above by means of one or more of the above-mentioned multiple access and diversity techniques. Alternatively or additionally, each wireless link may further comprise a transmission slot indicator to indicate the time slot at which the wireless link is scheduled and/or a transmission channel indicator to indicate the channel to which the one WDC unit and the one WM unit have to tune to. By assigning transmission slot indicators to the at least two wireless links, it is possible to schedule channel access in the on-board aircraft network cell described above by means of one or more of the above-mentioned multiple access and diversity techniques. It is to be noted that all of the aforementioned information (link number, link direction, transmission slot indicator and/or transmission channel indicator) may be assigned by one or more entities responsible for scheduling or organising the radio channel access. For example, such entity may be the at least one WM unit, the at least two WDC units, and/or a further entity of the wireless communication network such as a server unit or other control unit. In accordance therewith, each link can be attributed by the scheduling process with all information necessary to ascertain a well-working network.
The WDC units may be configured to serve as a bridge between the at least one WM unit and a wired on-board aircraft network. The wired on-board aircraft network may be connected to a server unit provided on-board the aircraft such as an avionics server. In this way, a reliable and robust connection to an on-board server unit such as the avionics server can be provided. The server unit may provide flight related control and cabin system functionality, for example.
In a fourth embodiment, an on-board aircraft wireless communication network is provided. The on-board aircraft wireless communication network comprises at least one on-board aircraft network cell as described herein. The on-board aircraft wireless communication network may comprise a plurality of on-board aircraft network cells as described herein. The on-board aircraft wireless communication network may be connected to a wired on-board aircraft network. In this way, for each of the at least one WM unit, at least two wireless links may be available for communication with an on-board server unit such as the avionics server.
The specific network topology, i.e., at least one on-board aircraft network cell comprising at least two spatially separated WDC units, allows a WM unit inside such a cell to communicate with the on-board server such as an avionics server via two or more wireless links (that may also be referred to as wireless communication links), one link for each WDC unit inside the cell.
It is conceivable that a WM/WDC unit can only use one of these wireless links at a time for wireless transmission of a data packet from the WM unit to the WDC unit or vice versa, except for multicast transmissions. A communication link may be considered to be associated with a WM unit, a WDC unit (space), a specific time slot (time), a radio channel (frequency) and a transmission direction.
In a fifth embodiment, an aircraft is provided. The aircraft comprises an on-board aircraft wireless communication network as described herein. The aircraft may further comprise a wired on-board aircraft network. The wired on-board aircraft network may be connected to a server unit provided on-board the aircraft such as an avionics server.
Still further, it is to be noted that the method aspects may also be embodied on at least one of the at least one WM unit, the at least two WDC units and any other suitable device comprising at least one processor and/or appropriate components for carrying out any one of the method steps. Thus, even if some of the above aspects are described herein with respect to the at least one WM unit or the at least two WDC units, these aspects may also be embodied in the on-board aircraft wireless communication network and/or the aircraft, or may be implemented as a method or as a computer program for performing or executing the method. Likewise, aspects described as or with reference to a method may be realized by suitable units (even if not explicitly mentioned) in the at least one WM unit, the at least two WDC units and/or any other suitable device, or by means of the computer program. All of the above described aspects may be implemented by hardware circuitry and/or by software.